Winter 2001

Science Bits

Does deforestation trigger regional drying?

According to most numerical models, large-scale deforestation
in the Amazon Basin should end up producing a warmer, drier
climate across the region. However, a new study of Amazonian
climate since 1950 contradicts that picture. A team from Iowa
State University examined data from three sources: the National
Centers for Environmental Prediction/NCAR reanalysis, the
Global Historical Climatological Network, and NOAA satellite
images of outgoing long-wave radiation. The team found that,
while temperatures have risen slightly, so has precipitation.
Rainfall amounts across the basin were roughly 20% higher in
1990 than in 1950, and satellite images show a rise in shower
and thunderstorm activity from 1970 to 1999. At the same time,
average sea-surface temperatures rose across the tropical
Pacific and Atlantic off equatorial South America. An
interdecadal analysis of the entire tropics shows an increase
in moisture converging on Amazonia. The Iowa State team is now
investigating whether the rise in nearby sea-surface
temperatures might be driving the warmer, wetter regime across
the Amazon. If so, they say, this trend could be suppressing or
obscuring the true impact of deforestation on regional climate.
The group suggests a closer look at the chain of physical and
biological mechanisms within the land-atmosphere interface in
Amazonia. They also recommend that climatic simulations of
land-use impacts be lengthy enough so that interdecadal climate
trends can be detected (many deforestation simulations only
span a few years). Iowa State geological and atmospheric
science professors Tsing-Chang "Mike" Chen and Eugene Takle and
graduate students Jin-ho Yoon and Kathryn St. Croix describe
their research in the October issue of the Bulletin of the
American Meteorological Society.

Iowa State University

Air-quality monitor from UC-Davis deployed at World Trade Center site

The massive cleanup effort at the wreckage of the World Trade
Center in New York City has been assisted by air-quality
experts from the University of California, Davis. The
university's DELTA Group (for Detection and Evaluation of Long-
Range Transport of Aerosols) specializes in round-the-clock
measurement of aerosol size and composition. The WTC data are
being used to monitor potential health threats such as
inhalable particles, toxic metals, asbestos, and byproducts of
burning plastic. On the roof of a building about a mile north
of ground zero, a sampler has been taking measurements in eight
size ranges, from more than 5.0 micrometers down to
0.090.24 micrometers. Particulates in the smallest range
are most likely to go far into the lungs, according to UC-Davis
professor emeritus Thomas Cahill. Early data showed strong
evidence of particulates in this size range, says Cahill. The
DELTA data have been helping the cleanup managers to choose
appropriate safety measures at the site, such as what workers
should wear (face masks, respirators, specific filters, body
suits) and how long people can safely work. Analyses have been
conducted by UC-Davis assistant research engineer Steven Cliff,
chemistry professor Peter Kelly, engineering professor James
Shackelford, and (from Lawrence Livermore National Laboratory)
project investigator Graham Bench. The sampler is expected to
be on site for about six months. Before it came to New York,
the sampler was in Korea as part of the most recent Aerosol
Characterization Experiment (ACE-Asia).